Soft Substrate Up-regulates the Interaction of STIM1 with Store-operated Ca2+Channels That Lead to Normal Epithelial Cell Apoptosis

Publisher Website
Google Scholar
Abstract
We have demonstrated that soft substrate induced apoptosis in polarized cells, but not in transformed cells by disturbance of Ca2+homeostasis. This study aims to further investigate the regulatory mechanisms underlying the disruption of Ca2+-signaling integrity in soft substrate–induced epithelial apoptosis. Soft substrate up-regulated the store-operated Ca2+(SOC) entry across the plasma membrane of normal cervical epithelial cells, which resulted in increased cytosolic Ca2+levels. Concomitantly, soft substrate induced the aggregation and translocation of stromal interacting molecule 1 (STIM1) toward the cell periphery to colocalize with Orai1, an essential pore subunit of SOC channel, detected by fluorescence resonance energy transfer approach and confocal image analyses. The disturbed Ca2+homeostasis resulted in the activation of μ-calpain, which cleaved α-spectrin, induced actin disorganization, and caused apoptosis. In contrast, soft substrate did not disturb Ca2+homeostasis or induce apoptosis in cervical cancer cells. Chelating extracellular Ca2+by EGTA and down-regulated SOC entry by small interfering RNA targeting STIM1 or inhibitors targeting Ca2+-binding site of calpain significantly inhibited soft substrate–induced activation of μ-calpain and epithelial cell apoptosis. Thus, soft substrate up-regulates the interaction of STIM1 with SOC channels, which results in the activation of μ-calpain and subsequently induces normal epithelial cell apoptosis.